If the turnover of the llp exceed 40 lakhs rupees and contributions exceeds 25 lakhs rupees then you should follow annual filing and audit otherwise not required
I think , You can file 18 months return ( from 1/10/2019 to 31/3/2021 ) by 31/3/2021, however you have to confirm on MCA web site or MCA office contact no .
Check out on Ministry of Corporate Affaires web site ( GoVT of India ) in FAQ section or you can contact them on phone, wherein you have to file return .
In case LLP has been incorporated on or after 1st October of the financial year, then LLP can close its first financial year either on the coming or next 31st March i.e. LLP files its first financial year details for 18 months.